Cryptology, or even scrambling, or even encryption, consists in using secret conventions to transform information that can be understood by third parties into information that is unintelligible to third parties, or in carrying out the reverse operation, called decryption, using means known for this purpose.
In packet telecommunication networks, data packets are transmitted. A data packet conventionally comprises a datum containing transport information which is mainly linked to the transport processing in the network, and so-called payload data containing information that is mainly linked to the content of the message to be transmitted and that must be routed to the recipient.
In the existing networks, there are already numerous data encryption methods. Some of these methods offer to encrypt data packets at the transport data level.
Thus, in the field of Internet type networks, a protocol called IPsec, standing for “Internet Protocol security”, is known, and is defined in the standard document “Security Architecture for the Internet Protocol”, reference RFC 2401 (RFC standing for “Request For Comments”). Also known is a protocol named SRTP, standing for “Secure Real-Time Transport Protocol”, which is defined in the standard document “The Secure Real-time Transport Protocol” referenced RFC 3711. Protocols of this type are known and suitable for encrypting data transmitted using an IP type protocol. They exhibit the drawback of not being adapted easily to other transport types such as, for example, the transport of multimedia files or even DVB (Digital Video Broadcast) type broadcasting in the networks.
Other solutions propose encryptions that are designed for and suited to encrypting data transmitted using a DVB type protocol. Particularly well known is an encryption function named DVB-CSA (CSA standing for “Common Scrambling Algorithm”), defined in a document referenced ETR 289 (standing for “European telecommunications standards institute Technical Report”). Such a function is particularly well-suited to use in an MPEG-2 TS (standing for MPEG2 Transport Stream, an audio and video sequence compression standard) type data stream.
One drawback of this type of encryption is that it does not specify a synchronization mechanism between data to be encrypted and encryption keys for use of such an encryption method in a transmission of data that is not encoded according to the MPEG-2 TS standard. Furthermore, a DVB-CSA type encryption function is not suited to encrypting audiovisual type payload data of variable sizes.
There are also encryption functions produced at the transported payload data level. Particularly well known in a multimedia network is a specification named ISMA Encryption and Authentication (ISMA standing for “Internet Streaming Media Alliance”), whereby multimedia type payload data can be encrypted. The ISMA encryption method entails modifying the header of each multimedia datum in order to include in it specific encryption information for synchronization purposes. This encryption information normally consists of public parameters such as, for example, a unique identifier for each datum to be encrypted or even an encryption key indicator.
One drawback of this type of encryption method is that it adds synchronization information which creates a not inconsiderable overhead in the transmission of such encrypted data. Such a method also poses problems of compatibility with existing software resulting from the modification of the header of the encrypted data.
Thus, there is an interest in defining an encryption method enabling the data transported in the telecommunication network to be encrypted in a way that is independent of the transport layer of the network used, without generating an overhead associated with this encryption method.